1. Field of the Invention
The invention relates to a explosive safe-arming apparatus for use in a perforating gun for oil and gas well wireline operations.
2. Description of the Prior Art
The perforating guns most commonly used in present-day wireline service operations are typically comprised of an elongated fluid-tight body or so-called "enclosed carrier" which houses one or more shaped explosive charges and the necessary accessories for selectively detonating these charges from the surface. One typical style of such carriers employs an expendable, thin-walled steel tube which has reusable upper and lower heads fluidly sealed in each end of the tubing. Other common types of enclosed carriers have heavy, explosion-resistant walls so that the carrier can be retrieved. This latter type of carrier is ordinarily provided with a removable head or an access port to accommodate the installation of the shaped charges and their associated detonating components.
Those skilled in the art will recognize, of course, that a typical shaped charged perforating gun ordinarily poses no serious hazards so long as there is either a spatial interruption in the explosive detonating train for the gun or the electrical wiring to the detonating train is suitably disconnected. Thus, the usual practice is to substantially complete the assembly of a given gun, but in some approved manner, leave the gun in a relatively safe or "disarmed" condition until just before it is to be operated. Another such safe-handling technique is simply not to install the electrically-initiated detonator for a given gun until it is being prepared for immediate operation.
It will be appreciated, however, that such typical safe-handling techniques are not entirely satisfactory. For example, where a perforating gun is disarmed by temporarily removing part of its explosive detonating train, there are still safety and logistic problems involved in handling the removed explosive. Moreover, where last minute electrical connections or other detailed preparations are required to ready the perforator for firing, these final steps often must be made under severe environmental conditions which can easily contribute to either a malfunction or even an unsafe or improper operation. Accordingly, it is most desirable to not have any electrical connections made in the field, but rather at the factory or in a field office.
One approach to solve the foregoing described problems may be found in U.S. Pat. No. 4,011,815, issued on Mar. 15, 1977, to Jose B. Garcia. This patent discloses a safe-handling arming apparatus wherein a receptor detonating explosive is fixedly disposed within an enclosed carrier, and a donor detonating explosive is movably disposed in a spaced relationship from the receptor detonating explosive, whereby the two explosives may be brought within relative detonating proximity of one another. In another embodiment of the safe-handling arming apparatus disclosed in the Garcia patent, the receptor detonating and donor detonating explosives are in an end-to-end parallel relationship, and a movable barrier member is disposed between the two explosives. By removing the barrier, the two explosives are in detonating proximity of one another.
The safe-handling arming apparatus of the Garcia patent suffers from some of the disadvantages previously described with respect to other devices, in that in order to arm the detonating train, it is necessary for the operator to contact the donor explosive to move it into engagement with the receptor explosive. With regard to the other embodiment of the Garcia patent, wherein the donor and receptor explosives are in an end-to-end parallel relationship with a barrier member removably disposed therebetween, an operator does not have to handle the donor explosive to arm the gun. However, in that embodiment an additional component for the perforating gun is required to support the explosives in position, as well as, the use of a shock-attenuating material to make that additional component. Furthermore, the section apparatus was not readily adaptable for use in all sizes of perforating guns, and the perforating gun components required modification to accept that safe-handling apparatus.
Accordingly, prior to the development of the present invention, there has been no safe-arming apparatus for use with perforating guns which is: readily adaptable for use with existing perforating guns, without modification thereto; does not require last minute electrical connections to be made in the field to ready the perforator for firing; provides additional operator safety, insofar as the operator does not have to handle the donor detonator explosive material; is inexpensive to manufacture; and efficient and easy to use. Therefore, the art has solved an efficient, safe and inexpensive safe-arming device for perforating guns, which can be used with conventional perforating guns without modification thereto.